my desktop pc is very slow?

Similar to other answers:
Make sure you have plenty of space free on your C: drive.
When defragging, you need to keep rerunning it over and over until it stops improving (with XP in normal startup mode usually this is 2 or 3 attempts).
Personally I would recommend a free app called myDefrag and choose to run the 'monthly scan'. www.mydefrag.com/
As Peccavi mentioned, there are lots of free spyware removal tools out there and it's just a matter of personal taste which one you use. I have moved on from Spybot S&D and instead use one called Super AntiSpyware www.superantispyware.com/ (seems to find more). If you go for something else then be very careful as there are a lot of fake spyware removal tools out there (which are actually infested with trojans or other malware).
I assume you have up to date antivirus? If not then I'd recommend a good free one called Avira AntiVir http://www.free-av.com/ (I find more reliable than AVG / Avast).
Lastly as others have mentioned, over time more and more apps creep into your startup list (legitimate apps and nasties). The problem is there are so many different startup locations in Windows. I'd recommend a free app called Autoruns which will actually show you everything that starts up (and lets you remove them) http://technet.microsoft.com/en-us/sysinternals/bb963902.aspx.
Be very careful removing items from starting up if you don't know exactly what it is you're removing, as there's a lot of system stuff in there you won't recognise but is still required. Prob worth doing a system restore snapshot before making any changes:http://www.microsoft.com/windowsxp/using/helpandsupport/getstarted/ballew_03may19.mspx

Best of luck

Steve I
July 2010

Try a free maintenance utility like Advanced System Care. You can download it from www.download.com

John's Help
July 2010

If it ran fine when it was new then it had enough memory then... there is little point in adding more memory unless you are now running "heavy" software like a big database or a demanding game. More memory will not make much/any difference to start up times.

Over time lots of things (some good software and some malicious software) get themselves an entry in the startup list - without your knowledge. These programmes load or part load at start time - little by little the process of starting up becomes longer and longer.

My start list has about 20 entries in it but only 3 of them are selected to run at start time.

Find out how to prune your startup list and clear out (unselect) everything except anything you believe to be important - security software for instance.

Get hold of a malware-checker (I use Spybot Search & Destroy - free - but there are others) and run it monthly - first time you run it it may find over 100 naughty bits of S/W.

Get hold of Piriform's CCleaner (free) and use the registry tool to tidy up the machine's registry.

Defrag annually - clean registry annually - run spybot monthly - avoid file sharing sites - and now and again check what's been ticked in the startup list.

Process Explorer is another useful free tool but it does no more than Task Manager - just gives prettier pictures.

Good luck...

Peccavi
July 2010

Fit more memory (RAM).

T
July 2010